1. Field of the Invention
The present invention relates to a magnetic head device for a recording and reproducing apparatus which is designed to travel a magnetic tape in both directions at a high speed for the purpose of keeping storage capacitance larger and a recording density more integrated.
2. Description of the Related Art
A magnetic head device which applicants know, capable of recording and reproducing an information signal on and from a magnetic tape, includes a magnetic head, a convexly curved sliding surface formed on a tip side of the magnetic head, a magnetic gap provided on the substantially central position of the convexly curved sliding surface, and guide rollers for guiding the magnetic tape along the convexly curved sliding surface. The area on which the magnetic tape keeps in contact with the convexly curved sliding surface is variable depending on the positional relation between the guide rollers and the convexly curved sliding surface. And the area with which the magnetic tape comes into contact does not occupy the overall width of the sliding area but only the central width located thereon.
When the magnetic tape is running along the convexly curved sliding surface at a high speed, a fluid lubrication effect brings about a gap (referred to as spacing) between the convexly curved sliding surface and the magnetic tape. The spacing distributed on the left side of the magnetic gap is greatly different from that distributed on the right side thereof. In such spacing distribution, the spacing located on the magnetic gap may be made larger by a disturbance such as vibrations. As the spacing becomes larger, the output loss is made larger. Hence, it is impossible to realize stable short wave recording for improving a recording density by the device which has the foregoing arrangement.
For improving the spacing distribution, a known magnetic head device, as disclosed in the Japanese Patent Application Laying Open (KOKAI) No. 60-124052, is designed to provide an angle .alpha. formed between a straight line connecting both ends of a convexly curved sliding surface of a magnetic head, that is, a chord and tangent drawn at the end portion of the convexly curved sliding surface (referred to as a tangent angle) to be smaller than an angle .beta. formed between the chord and the inflow direction of a magnetic tape (referred to as a winding angle), and a ratio .beta./.alpha. to be in the range of 1.2 to 2.5. The design makes it possible to obtain substantially uniform spacing distribution having no inclination or unevenness on the overall width of the convexly curved sliding surface, resulting in keeping the spacing located on the magnetic gap substantially stable even if a disturbance such as vibrations takes place. Hence, it is possible to obtain a stable electromagnetic conversion characteristic.
Recently, this type of the magnetic tape has been keeping storage capacitance larger and tape transfer faster. As the recording density becomes higher, therefore, focus has been put on a head touch between a magnetic head and a magnetic tape. Smaller spacing has been requested than the foregoing substantially uniform spacing distribution having no inclination and unevenness.
The foregoing arranged device, however, cannot always offer an excellent electromagnetic conversion characteristic when running the magnetic tape at a high speed.
The reason why those related arts cannot meet the fine spacing required by the recent magnetic tape will be explained as follows. For example, according to the relation between a head output and tension (referred to as tape tension) applied on the magnetic tape when a test is done by use of the above magnetic head device in the state of setting the ratio .beta./.alpha. to 2.0, as the tape tension increases, the head output becomes larger. Then, when the tape tension reaches a value Ta, the head output is gradually decreased along the increase of the tape tension. That is, the spacing is variable depending on the tape tension, so that the head output varies not only as the ratio .beta./.alpha. but also as the tape tension.
And according to the relation between a ratio .beta./.alpha. and an output given by the test performed under the condition that the winding angle .beta. of the magnetic tape and the tangent angle .alpha. of the magnetic head is being changed, the head output becomes maximum when the ratio .beta./.alpha. stays in the range of 3 to 4. Here, the magnetic tape speed in reading is 90 IPS. And the results of the other tests indicate their own optimal ratio .beta./.alpha. values for the maximum head output.
As is apparent from the above description, if the ratio .beta./.alpha. is adjusted to be in the range of 1.2 to 2.5, the resulting spacing does not necessarily meet the requested small spacing. In particular, the lower tape tension results in causing considerably large spacing, thereby lowering the output and being unable to keep a recording density sufficiently higher.